The first combined diode detector and audio amplifier to be produced. It was developed by RCA in 1931 but was not announced until the middle of 1932. The two diodes and the triode share a common cathode. One diode is usually used as the signal detector; the other is used to generate the automatic gain control (AGC) voltage. The triode section is used as the first audio amplifying stage. It has a 2.5 volt indirectly heated cathode.
The advent of this type of valve and the remote cut-off pentode made automatic gain control practical and economical. The 55 was followed by numerous electrically similar types in all bulb configurations until the end of the receiving valve era in the 1960s.
Manufacturer: RCA Radiotron Co., Harrison, NJ, USA.

Physical Description

Shouldered bulb with top cap and 6 pin American style base.

More Information